Within the literature, toddlers who demonstrate delayed onset and progression of expressive language in conjunction with otherwise age-appropriate development are known as "late talkers." Though many late talkers ultimately achieve language outcomes within the normal range by early school age, a subset of this group of children is considered at risk for developing Specific Language Impairment (SLI), a developmental disorder that negatively impacts social and academic performance in childhood and adolescence. The specific underlying processes that result in the linguistic deficits observed in SLI remain the subject of theoretical debate. One set of theoretical accounts focuses on nonlinguistic contributors such as limitations in processing that impair the ability to integrate and manage various aspects of the linguistic system. Processing limitations that are evidenced in children with SLI in later childhood may originate in early language development and may contribute to the difficulties that late talkers display in acquiring language. Though late talkers present with largely intact receptive vocabularies, questions remain with respect to more subtle aspects such as the time course of comprehension. This project will explore language processing as it relates to vocabulary comprehension using preferential looking tasks that have been successfully applied to typical and clinical populations. A group of toddlers who have been identified as late talkers will be compared to groups of age-matched and comprehension-matched peers with respect to familiar and novel word comprehension tasks as well as traditional measures of vocabulary comprehension and production. Frame-by-frame coding of eye movements within preferential looking tasks will allow us to capture finely grained differences in response time and accuracy of novel and familiar word comprehension across the three groups and have the potential to reveal processing differences that have gone largely unidentified in late talkers. In addition, careful manipulation of the phonotactic characteristics of novel stimuli will provide information with respect to young childrens1 sensitivities to the frequency of occurrence of sound patterns in the environment as related to novel word learning and vocabulary size. Public Health: The identification of differences in accuracy and response latency within these comprehension tasks could ultimately serve as predictors of later language performance and assist in the early identification of toddlers at risk for Specific Language Impairment. In addition, the successful use of looking preference procedures with late talkers will lay the groundwork for the application of this approach to other clinical populations such as children on the autism spectrum. [unreadable] [unreadable] [unreadable] [unreadable]